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Old 12-22-2018, 12:50 AM   #1
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Finishing basement


Hey all! My wife and I bought a brand new home this Summer with an unfinished basement. We are located in Minnesota and the home is a split level. Half of the basement is below grade. As you can see from the pictures, the half wall sticks out from the studs and insulation by about an 1 1/2". I think I have decided I am just going to finish the basement with a ledge as this will save a lot of money I believe. I have a few questions before even starting and hoping I can rely on some of you through this process. What is the best way to insulate the lower area I will be framing? Is it best to use adhesive and rigid foam on the concrete itself before framing so there is continuous insulation? What about between the studs? I've attached a few pictures.
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Finishing basement-15454577324605375706813385771296_1545457750169.jpg   Finishing basement-1545457762479402332344753004328_1545457779007.jpg  
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Old 12-22-2018, 01:10 AM   #2
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Re: Finishing basement


You don't want the would of your wall to touch the foundation.
We nail a 2x4 with top about 6" above the foundation. Depending on how much the foundation is sticking into the room maybe a 2x4 wall just up against that 2x4 or a 2x6 or 2x8 on the flat on top of the 2x4, what ever you need to get your wall just a little away from the foundation.
Sill gasket under the bottom plate.
Insulate the 2x4 wall and drywall.
drop the ledge down under windows to the rough sill height just for the window.
If you have a door to the outside, stop the wall making it 45 degrees on the end to give the door a little more swing area.
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Old 12-22-2018, 03:40 PM   #3
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Re: Finishing basement


Yes foam will add some R value and allow you to keep out excess moisture. You want vapor semi-permeable, not semi-impermeable on the interior side of a block foundation basement in our climate zone. So that's a perm rating of 1.0-10, or less than 2 inch XPS, not 2 inch or greater XPS. A 2 inch XPS puts you into a .55 perm rating, or semi-impermeable. Once you put the foam up all around then frame bottom plates with pressure treated with a sill plate but the rest can be usual 2 x4 framing. If you seal off the wall completely you can use unfaced fiberglass and not worry about moisture. Or go rockwool but man itís expensive.

This is what I did and Iím very happy with the humidity and temp even when itís freezing outside.


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Old 01-08-2019, 02:00 PM   #4
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Re: Finishing basement


Quote:
Originally Posted by chadhyett View Post
Yes foam will add some R value and allow you to keep out excess moisture. You want vapor semi-permeable, not semi-impermeable on the interior side of a block foundation basement in our climate zone. So that's a perm rating of 1.0-10, or less than 2 inch XPS, not 2 inch or greater XPS. A 2 inch XPS puts you into a .55 perm rating, or semi-impermeable. Once you put the foam up all around then frame bottom plates with pressure treated with a sill plate but the rest can be usual 2 x4 framing. If you seal off the wall completely you can use unfaced fiberglass and not worry about moisture. Or go rockwool but man itís expensive.

This is what I did and Iím very happy with the humidity and temp even when itís freezing outside.


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what's the purpose of staying semi-permeable on the inside of a block wall, as you're suggesting here? The block will grab/retain moisture from the soil, but there shouldn't be any need for it to be able to dry to the interior, should there? Isn't that just contributing to excess moisture?

Admittedly, I go back and forth between feeling as though i have a good grasp on some of these building principles and having no clue -- with insulation layers and permeability being one of my worst subjects.

I could be sorely mistaken, and hopefully someone smarter than I points it out if i am, but lots of the latest articles I've seen suggest that drying to the inside is not necessary, and that enough R-value be added (XPS, for instance) to prevent any warm, interior air from hitting the cool block foundation and condensing.

OP, Maybe look into several inches of rigid XPS directly attached to the block, with a 2x4 stud wall in front of that. PT bottom plate, then regular dimensional for the rest. You'd just have to figure out how to handle the 1-1/2 difference at the transition/ledge so that it's not the weak point in your thermal layer. Extra insulation in the stud bays is your call at that point.

There are calculators that will tell you how thick your insulation layer must be to mitigate issues based on your climate zone.

Best of luck!
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Old 01-08-2019, 02:20 PM   #5
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Re: Finishing basement


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Originally Posted by alexjburkhardt View Post
what's the purpose of staying semi-permeable on the inside of a block wall, as you're suggesting here? The block will grab/retain moisture from the soil, but there shouldn't be any need for it to be able to dry to the interior, should there? Isn't that just contributing to excess moisture?



Admittedly, I go back and forth between feeling as though i have a good grasp on some of these building principles and having no clue -- with insulation layers and permeability being one of my worst subjects.



I could be sorely mistaken, and hopefully someone smarter than I points it out if i am, but lots of the latest articles I've seen suggest that drying to the inside is not necessary, and that enough R-value be added (XPS, for instance) to prevent any warm, interior air from hitting the cool block foundation and condensing.



OP, Maybe look into several inches of rigid XPS directly attached to the block, with a 2x4 stud wall in front of that. PT bottom plate, then regular dimensional for the rest. You'd just have to figure out how to handle the 1-1/2 difference at the transition/ledge so that it's not the weak point in your thermal layer. Extra insulation in the stud bays is your call at that point.



There are calculators that will tell you how thick your insulation layer must be to mitigate issues based on your climate zone.



Best of luck!


Everything that Iíve read says that you should allow any moisture to come out of the wall and dry inward. Check this out - https://buildingscience.com/document...ent-insulation


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Old 01-08-2019, 02:23 PM   #6
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Re: Finishing basement


Quote:
Originally Posted by alexjburkhardt View Post
what's the purpose of staying semi-permeable on the inside of a block wall, as you're suggesting here? The block will grab/retain moisture from the soil, but there shouldn't be any need for it to be able to dry to the interior, should there? Isn't that just contributing to excess moisture?


Everything that Iíve read says that you should allow any moisture to come out of the wall and dry inward. Check this out - https://buildingscience.com/document...ent-insulation



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Old 01-08-2019, 02:46 PM   #7
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Re: Finishing basement


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Originally Posted by chadhyett View Post
Everything that Iíve read says that you should allow any moisture to come out of the wall and dry inward. Check this out - https://buildingscience.com/document...ent-insulation


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Touche! I believe I've found that before as well.

I'll see your article from 2009 and raise you two from 2012 that combat this very issue from Building Science. Can't make this stuff up -- building science is quite the intriguing topic.

https://www.greenbuildingadvisor.com...-basement-wall

https://www.greenbuildingadvisor.com...apor-retarders

It seems that the main concern between the two viewpoints could be whether, in an effort to stay below a specified perm rating, enough r-value was not applied to control condensation in the inside. It's not necessarily either-or, there may be scenarios for both that could work, it just seems as though drying is not as important as initially thought.
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Old 01-08-2019, 06:00 PM   #8
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Re: Finishing basement


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Originally Posted by alexjburkhardt View Post
Touche! I believe I've found that before as well.



I'll see your article from 2009 and raise you two from 2012 that combat this very issue from Building Science. Can't make this stuff up -- building science is quite the intriguing topic.



https://www.greenbuildingadvisor.com...-basement-wall



https://www.greenbuildingadvisor.com...apor-retarders



It seems that the main concern between the two viewpoints could be whether, in an effort to stay below a specified perm rating, enough r-value was not applied to control condensation in the inside. It's not necessarily either-or, there may be scenarios for both that could work, it just seems as though drying is not as important as initially thought.


Well damn. I had not seen this. Thanks for sharing. Iím not about to rip out my assembly (plus drywall going up on Thursday) but good to know.


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